1. Field of the Invention
The present invention relates to an apparatus for controlling an ignition timing of an engine. More particularly, the present invention relates to an apparatus for controlling an ignition timing of an engine, which is capable of reducing the likelihood of backfires.
2. Description of the Relevant Art
When engine speed is decreased sharply, the ratio of fresh air to the volume of a cylinder is lowered. Hence, a charging efficiency decreases, so that the air/fuel ratio in the cylinder becomes lean. As a result, the possibility of backfires increases, such that a flame propagating speed becomes slow and flame spreads into an intake path.
Systems are known in the background art to decrease the likelihood of backfiring. For example, Japanese Patent Bulletin No. 2,646,216 discloses an ignition timing control system. In the background art, when sudden deceleration occurs, the ignition timing control advances the ignition timing (relative to a normal ignition timing) until a throttle is fully closed.
According to the background art, the ignition timing is advanced (relative to the normal ignition timing) until the throttle is fully closed, when sudden deceleration occurs. After the throttle is fully closed, the ignition timing is reset to the standard or normal ignition timing. In other words, the ignition timing is no longer advanced.
According to experiments conducted by the inventors, backfires occur most often in a sudden deceleration state. Backfires particularly occur when the throttle is suddenly opened from a no-load deceleration state.
Based upon the inventor""s experiments, it can be seen that the system of the background art has drawbacks. In the system of the background art, the ignition timing is reset from the advanced state to the normal state at the time when the throttle is fully closed. However, if the throttle is suddenly opened during a no-load deceleration state, backfires are likely to occur.
On the other hand, if the ignition timing is advanced after the throttle opening operation is detected at the time of sudden deceleration, the flame propagation speed just before the opening operation cannot be improved. When the ignition timing is advanced only on condition that the throttle is fully closed, poor engine performance results, particularly a xe2x80x9cknockingxe2x80x9d problem occurs.
It is an object of the present invention to solve one or more of the drawbacks associated with the systems and techniques of the background art.
It is an object of the present invention to provide an apparatus for controlling ignition timing of an engine, capable of effectively preventing backfires by a simple configuration.
These and other objects are accomplished by an apparatus for variably controlling an ignition timing of an engine in accordance with operating conditions of the engine, said apparatus comprising: a no-load deceleration state detector for detecting that an engine is in a no-load deceleration state; an engine speed detector for detecting an engine speed; and a controller advancing an ignition timing when said no-load deceleration state detector detects the no-load deceleration state and said engine speed detector detects the engine speed to be in a speed range.
Further, these and other objects are accomplished by an apparatus for variably controlling an ignition timing of an engine in accordance with operating conditions of the engine, said apparatus comprising: a standard ignition timing setting unit for providing standard ignition timing control signals during normal engine operating conditions; an advanced ignition timing setting unit for providing advanced ignition timing control signals during engine operating conditions prone to backfiring; a pulse generator sensing an angular position of a crankshaft, and outputting pulse signals; a converter for receiving the pulse signals from said pulse generator; a switch to selectively connect one of said standard ignition timing setting unit and said advanced ignition timing setting unit to said converter; and a no-load deceleration state determining unit controlling the operation of said switch, said no-load deceleration state determining unit causing said switch to connect said advanced ignition timing setting unit to said converter during engine operating conditions prone to backfiring and causing said switch to connect said standard ignition timing setting unit to said converter at other times, wherein the engine operating conditions prone to backfiring include a speed of the engine being within a predetermined speed range.
Moreover, these and other objects are accomplished by a method of controlling an ignition timing of an engine comprising the steps of: sensing if a throttle is fully closed; if the throttle is fully closed, determining an engine speed; if the engine speed is with a predetermined speed range, comparing a drop rate in the engine speed to a threshold value; and if the drop rate meets or exceeds the threshold value, advancing an ignition timing.
According to the present invention, the ignition timing is advanced at the time of sudden opening of the throttle from the no-load deceleration state, which is the time when backfires occur the most. As a result, combustion can be finished in a cylinder before an exhaust port is opened, so that the occurrence of backfires can be reduced or prevented, without deteriorating the operation of the engine, such as avoiding knocking.
According to the present invention, whether or not the engine is in the no-load deceleration state is determined on the basis of throttle angle and engine speed. Thus, a detector for detecting that the engine and the output shaft are disengaged from each other is unnecessary.
Alternatively, according to the present invention, by using the fact that the drop rate of the engine speed, at the time of no-load deceleration, is peculiar to each engine, whether or not the engine is in the no-load deceleration state can be determined on the basis of only the engine speed. Thus, a detector for detecting a throttle angle is also unnecessary.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.